WASHINGTON (AP) — A showdown looming, Republicans and Democrats groped for a compromise behind closed doors Monday over confirming stalled White House appointees in a dispute that threatened what little bipartisan cooperation remains in the Senate.

All 100 senators were invited to the rare closed-door meeting in the Capitol's Old Senate Chamber, just down the hall from where they normally debate the issues of the day with the public and news media in attendance.

Majority Leader Harry Reid insisted in advance that Republicans permit yes-or-no confirmation votes on all seven of the nominees at issue. If they won't, he declared, Democrats will change the Senate's rules to strip them of their ability to delay.

There was no formal response from Republicans, although Reid and Senate Republican leader Mitch McConnell met privately during the day. Officials said several possible compromises had been floated in various meetings and conversations.

"Maybe there's a little bit of a thaw," said Sen. John Thune, R-S.D., as he entered the meeting. "The leaders are continuing to talk, the White house is involved in discussions with some of our members. Nothing has resulted from that, but the fact that people are still talking is a positive."

Officials in both parties said there had been discussions about Republicans stepping aside to permit confirmation for nearly all of the seven, with Obama agreeing to submit a replacement for at least one of two stalled appointees to the National Labor Relations Board.

In a morning speech at the Center for American Progress, Reid said there was no room for a middle ground allowing votes on some but not all of the seven.

"Minor change, no big deal," he said then of the possible rules change. "My efforts are directed at saving the Senate from becoming obsolete."

Republicans counter that a rules change made unilaterally by one party would profoundly alter the Senate, where both parties pay tribute to maintaining minority rights that are far stronger than in the House. Rules changes generally are made with a two-thirds vote of the Senate, meaning they must be bipartisan.

"I guarantee you, it's a decision that, if they actually go through with it, they will live to regret," McConnell said last week of the Democrats.

At the core of the dispute is the minority party's power to stall or block a yes-or-no vote on nearly anything, from legislation to judicial appointments to relatively routine nominations for administration positions. While a majority vote is required to confirm presidential appointees, it takes 60 votes to end delaying tactics and proceed to a yes-or-no vote.

The Democrats are threatening to change the rules only as they apply to nominations for administration positions, not judges or legislation, although Reid appeared to hedge when asked what other changes he might want to make the Senate more effective. "Nothing right now," he said.

Sen. Jeff Flake, R-Ariz., noting he was elected to the Senate only last year, said that despite Reid's contention the change was potentially momentous. He said the need for confirmation means appointees must hear the concerns of individual senators in a way that is not the case with House members. He said the chances were strong that once the rules were altered, one party would expand the change to include "judicial nominees that have a lifetime tenure" or even legislation.

At the White House, spokesman Jay Carney said Obama believes "the Senate ought to function and hopes the Senate will figure out a way that the nomination process is appropriately streamlined."

For now, he noted, "We're talking here about executive branch nominees." But he quickly added, "We have big problems on the judicial branch nomination process too."

In its purest form, a Senate delay can mean a classic filibuster — such as when Sen. Strom Thurmond stood at his desk in 1957 and spoke for a few minutes longer than 24 straight hours in an unsuccessful attempt to prevent action on historic civil rights legislation.

In the past half-century, the filibuster has evolved, as have other means of stalling votes without requiring an around-the-clock speech that defies human endurance.

In the current case of Gina McCarthy, who was named to head the Environmental Protection Agency in March, Reid said during the day that Republicans had submitted more than 1,100 questions for her to answer about her plans at an agency they frequently criticize. He said they also refused to attend a committee hearing to vote on the nomination, forcing Democrats to summon a mortally ill Democratic Sen. Frank Lautenberg, D-N.J from home so enough lawmakers would be present to conduct business.

Reid said he called Lautenberg's wife, and said, "We have to have him here. And he literally on his deathbed came down here, unhooked the stuff that is keeping him alive, came down here from New Jersey." Lautenberg has since passed away.

In recent days, Republicans have signaled they will no longer attempt to block votes on several of the seven, including McCarthy, Labor Secretary-designate Tom Perez and Fred Hochberg to head the Export-Import Bank. They have refused to agree to the same for Richard Cordray, named in 2011 to head a newly created Consumer Finance Protection Bureau, or Richard Griffin and Sharon Block, appointed the same year to the National Labor Relations Board. Also stalled is Mark Pearce, nominated this year to a new term as head of the NLRB, which rules on collective bargaining disputes between unions and employers.

Cordray, Griffin and Block are in their posts, after Obama bypassed the Senate and gave them recess appointments. But an appeals court has ruled the two NLRB appointments are invalid, raising the prospect that all of their actions to date could be voided, and the Supreme Court has agreed to hear an appeal.

Last week, McConnell urged the administration to name two replacements for Griffin and Block, whom he called tainted appointments, and pledged quick consideration. Time is particularly significant in connection with the NLRB, because Pearce's current term expires at the end of the month. That would leave only two of five board's positions filled, not enough for it to issue rulings.

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